Diseases related to cigarette smoking, such as lung disease, heart disease and cancer, claim an estimated 400,000 lives each year. The combustion of tobacco produces poisons and carcinogens that present a significant health hazard for smokers and non-smokers alike. Nicotine is a principal component of tobacco, and the most pharmacologically active. It is physically addictive, making it extremely difficult for a smoker to quit.
Smoking a cigarette delivers nicotine vapors to the lungs, where nicotine is rapidly absorbed through the arteries and delivered to the brain. Nicotine interacts with nicotine cholinergic receptors in the brain to induce the release of neurotransmitters and produce an immediate reward—the “rush” that smokers experience—that is associated with a rapid rise in blood level. A persistent stimulus is also produced, and is associated with a high blood level of nicotine. As such, the dopaminergic reward system is activated which eventually results in nicotine dependency. Complex behavioral and social aspects of smoking, e.g., the hand-to-mouth ritual, etc., are also habit-forming.
A therapeutic approach to aid in smoking cessation is to provide the smoker with nicotine from sources other than cigarettes. Nicotine can be administered orally. However, after oral administration it is absorbed from the gut into the portal blood and degraded promptly by the liver. Nicotine can also be administered parenterally, e.g., intravenously, transcutaneously, muscosally, etc. Although preparations of nicotine appropriate for intravenous administration have been available for some time, intravenous cannulation as a means for gaining access to the circulation for the administration of nicotine on demand is not a socially acceptable alternative to cigarette smoking. There are also a number of commercially available nicotine replacement therapies that deliver nicotine to the systemic circulation via absorption through mucosal membranes or the skin. These include nicotine-containing chewing gum, sachets, transdermal patches, capsules, tablets, lozenges, nasal sprays and oral inhalation devices.
In particular, nicotine delivery via inhalation offers the benefit of addressing the psychological component of cigarette smoking in addition to the physiological dependence on nicotine. Nicotine inhalation systems release nicotine as a vapor (see U.S. Pat. Nos. 5,167,242; 5,400,808; 5,501,236; 4,800,903; 4,284,089; 4,917,120; 4,793,366), aerosol (see U.S. Pat. Nos. 5,894,841; 5,834,011) or dry powder (see U.S. Pat. No. 5,746,227) when air is inhaled through the inhaler. A droplet ejection device (U.S. Pat. No. 5,894,841) has also been described that delivers a controlled dose of nicotine via inhalation. These systems deliver low doses of nicotine to the mouth and throat, where nicotine is absorbed through the mucosal membranes into the circulation. Some inhalation therapies feature devices that simulate or approximate the look, feel and taste of cigarettes.
Currently available nicotine replacement therapies, such as transdermal and buccal systems where absorption occurs slowly, provide a low, steady-state blood level of nicotine to the patient without the early nicotine concentration spike that occurs due to immediate, arterial delivery of nicotine to the brain. Thus, the goal of these therapies is to eliminate the immediate, pleasurable effects associated with smoking while still alleviating the nicotine withdrawal effects until complete cessation of nicotine is physically and psychologically possible for the patient. The perceived advantage of these therapies is that the likelihood of abusing the nicotine delivery device (e.g., transdermal patch, nicotine chewing gum, nicotine inhalers, etc.) is very low. However, it is believed by some that it is because of this complete lack of “rush” experienced by the patient, that the success rates of these conventional therapies are not higher than they are.
Thus, the need remains for a smoking cessation therapy that delivers a precise dose of nicotine directly to the lungs and, therefore, directly into the arterial circulation in a profile that mimics the blood levels achieved by cigarette smoking-providing an initial sharp rise in blood level followed by a slow release of nicotine-making it possible for the user to be weaned off of nicotine and to quit smoking.